1. Field of the Invention
The present invention relates generally to television receivers and, more particularly, is directed to a television receiver of the so-called picture-in-picture type in which a sub-picture screen is displayed within a main picture screen in a picture-in-picture fashion.
2. Description of the Prior Art
In the prior art, there is known a television receiver of a so-called picture-in-picture type in which a sub-picture screen is displayed within a main picture screen in an inset fashion.
The picture-in-picture type television receiver is provided with a main tuner for forming, for example, a main picture video signal and a sub-tuner for forming a sub-picture video signal. In such a picture-in-picture type television receiver, the pictures displayed on the main and sub-picture screens can be exchanged with each other by exchanging the channel selection data of the main picture tuner and the sub-picture tuner (see Japanese published utility model application No. 60-17974).
In such a picture-in-picture type television receiver, it may be desired that a picture based on a high frequency input signal supplied from an auxiliary input terminal, for example a descrambler for receiving a pay television broadcast or the like, can be displayed in addition to the picture based on the video signal supplied through the television antenna. In this case, the antenna input and the high frequency input from the auxiliary input terminal must be switched. In order to omit a switching circuit, a circuit which employs a single switching circuit as shown in FIG. 1 has been proposed.
Referring to FIG. 1, an antenna input from an antenna AT and the high frequency input from an auxiliary input terminal 2 are supplied to a switching circuit 3. The output from this switching circuit 3 is supplied to a main tuner 5M and the antenna input from the antenna AT is supplied to a sub-tuner 5S. With the above circuit arrangement, when the high frequency input from the auxiliary input terminal 2 is supplied to the main tuner 5M by switching the switching circuit 3, the picture based on the high frequency input is displayed on the main picture screen Sm of the cathode ray tube 18.
With the circuit arrangement shown in FIG. 1, when the antenna input from the antenna AT is supplied to the main tuner 5M and the picture based on this antenna input is displayed on the main picture screen, the pictures displayed on the main screen Sm and the subpicture screen Ss can be exchanged with each other by exchanging the channel selection data of the main and sub-tuners 5M and 5S as described above. However, when the high frequency input from the auxiliary input terminal 2 is supplied to the main tuner 5M and the picture based on this high frequency input is displayed on the main picture screen, the pictures displayed on the main and sub-picture screens can not be exchanged with each other. This is because the sub-tuner 5S is not supplied with the high frequency input from the auxiliary input terminal 2. Accordingly, when the picture based on the high frequency input from the auxiliary input terminal 2 is displayed on the main picture screen and a command for exchanging the pictures displayed on the main and sub-picture screens is issued, an exchange of the channel selection data of the main and sub-tuners 5M and 5S should be inhibited. Further, when the channel selection data of the main and sub-tuners 5M and 5S are inhibited from being exchanged with each other, some warning should be given to the user so that the user will not become anxious when the pictures are not exchanged.